In a process of manufacturing a semiconductor device, various films are formed as, for example, an insulating film, a protective film, and an electrode film. Plasma CVD has been known as a method for forming such various films by exciting a film-forming gas by plasma to form a predetermined film on a substrate.
For example, Japanese Patent Laid-Open Publication No. 2009-246129 discloses a technique of supplying a silicon source gas, a nitrogen-containing gas, and an argon gas, which is a plasma generating gas, into a chamber, and forming a silicon nitride film by CVD.
The argon gas as the plasma generating gas is not essential, but may be used for stably generating the plasma. Further, Japanese Patent Laid-Open Publication No. 2011-077323 discloses that other rare gases may be used as the plasma generating gas. In fact, however, argon gas is used as the plasma generating gas in most cases.